Vulkan Runtime

TVM supports using Vulkan compute shaders to execute queries. Each computational kernel is compiled into a SPIR-V shader, which can then be called using the TVM interface.

Vulkan Features, Limits

Since different Vulkan implementations may enable different optional features or have different physical limits, the code generation must know which features are available to use. These correspond to specific Vulkan capabilities/limits as in Vulkan Capabilities Table. If unspecified, TVM assumes that a capability is not available, or that a limit is the minimum guaranteed by the Vulkan spec in the Required Limits section.

These parameters can be either explicitly specific when defining a Target, or can be queried from a device. To query from a device, the special parameter -from_device=N can be used to query all vulkan device parameters from device id N. Any additional parameters explicitly specified will override the parameters queried from the device.

Vulkan Capabilities

Target Parameter	Required Vulkan Version/Extension	Parameter Queried	Default Value
supported_subgroup_operations	Vulkan 1.1+	VkPhysicalDeviceSubgroupProperties::supportedOperations	0 (interpreted as VkSubgroupFeatureFlagBits)
max_push_constants_size		VkPhysicalDeviceLimits::maxPushConstantsSize	128 bytes
max_uniform_buffer_range		VkPhysicalDeviceLimits::maxUniformBufferRange	16384 bytes
max_storage_buffer_range		VkPhysicalDeviceLimits::maxStorageBufferRange	227bytes
max_per_stage_descriptor_storage_buffer		VkPhysicalDeviceLimits::maxPerStageDescriptorStorageBuffers	4
supports_storage_buffer_storage_class	VK_KHR_storage_buffer_storage_class		false
supports_storage_buffer_8bit_access	VK_KHR_8bit_storage	VkPhysicalDevice8BitStorageFeaturesKHR::storageBuffer8BitAccess	false
supports_storage_buffer_16bit_access	VK_KHR_16bit_storage	VkPhysicalDevice16BitStorageFeaturesKHR::storageBuffer16BitAccess	false
supports_float16	VK_KHR_shader_float16_int8	VkPhysicalDeviceShaderFloat16Int8FeaturesKHR::shaderFloat16	false
supports_float64		VkPhysicalDeviceFeatures::shaderFloat64	false
supports_int8	VK_KHR_shader_float16_int8	VkPhysicalDeviceShaderFloat16Int8FeaturesKHR::shaderInt8	false
supports_int16		VkPhysicalDeviceFeatures::shaderInt16	false
supports_int64		VkPhysicalDeviceFeatures::shaderInt64	false

As of May 2021, not all Vulkan implementations are supported. For example, support for 64-bit integers is required. If a Vulkan target is not supported, an error message should be issued during SPIR-V code generation. Efforts are also underway to remove these requirements and support additional Vulkan implementations.

SPIR-V Capabilities

Some of the device-specific capabilities also correspond to SPIR-V capabilities or extensions that must be declared in the shader, or a minimum SPIR-V version required in order to use a feature. The TVM-generated shaders will declare the minimum set of extensions/capabilities and the minimum allowed version of SPIR-V that are needed to execute the compiled graph.

If the shader generation requires a capability or extension that is not enabled in the Target, an exception will be raised.

Vulkan Capabilities

Target Parameter	Required SPIR-V Version/Extension	Declared Capability
supported_subgroup_operations	SPIR-V 1.3+	Varies, see VkSubgroupFeatureFlagBits
supports_storage_buffer_storage_class	SPV_KHR_storage_buffer_storage_class
supports_storage_buffer_8bit_access	SPV_KHR_8bit_storage	StorageBuffer8BitAccess
supports_storage_buffer_16bit_access	SPV_KHR_16bit_storage	StorageBuffer16BitAccess
supports_float16		Float16
supports_float64		Float64
supports_int8		Int8
supports_int16		Int16
supports_int64		Int64

Vulkan-Specific Environment Variables

Both the SPIR-V code generation and the Vulkan runtime have environment variables that can modify some of the runtime behavior. These are intended for debugging purposes, both to more easily test specific code paths, and to output more information as needed. All boolean flags are true if the environment variable is set to a non-zero integer. An unset variable, the integer zero, or an empty string are all false boolean flags.

• TVM_VULKAN_DISABLE_PUSH_DESCRIPTOR - A boolean flag. If true, TVM will explicitly allocate descriptors, and will not use the VK_KHR_push_descriptor or VK_KHR_descriptor_update_template extensions. If false, TVM will decide whether to use these extensions based on their availability.

• TVM_VULKAN_DISABLE_DEDICATED_ALLOCATION - A boolean flag. If true, TVM will not mark memory allocations as being dedicated allocations, and will not use the VK_KHR_dedicated_allocation extension. If false, TVM will decide whether memory allocations should be marked as dedicated based on the VkMemoryDedicatedRequirements for that buffer.

• TVM_VULKAN_ENABLE_VALIDATION_LAYERS - A boolean flag. If true, TVM will enable Vulkan validation layers that the device supports. If false, no validation layers are enabled.

• TVM_VULKAN_DISABLE_SHADER_VALIDATION - A boolean flag. If true, the SPIR-V shader validation done with spvValidate is skipped. If false (default), all SPIR-V shaders generated by TVM are validated with spvValidate.

• TVM_VULKAN_DEBUG_SHADER_SAVEPATH - A path to a directory. If set to a non-empty string, the Vulkan codegen will save tir, binary SPIR-V, and disassembled SPIR-V shaders to this directory, to be used for debugging purposes.